This invention concerns an optical pickup position control method that is used in an optical disk device that, in order to record and/or play information by shining an optical spot from an optical pickup onto an optical disk, uses a stepping motor to control the relative position of said optical disk and said optical pickup and is used if the relative position of the optical disk and optical pickup are to be open-loop-controlled.
In recent years, from CDs, CR-ROMs, etc., high-information-recording-density DVDs, DVD-ROMs, DVD-Rs, etc. have come to be used as the optical disk in optical disk devices that record and/or play information by shining an optical spot from an optical pickup onto an optical disk. With such a high-recording-density optical disk, it is necessary to adjust the relative position of the optical disk and optical pickup with high precision. If tilt control between the disk and pickup is to be achieved, because the margin with respect to the skew of the optical disk is reduced, position control is achieved in which a stepping motor is used to adjust the skew angle of the optical pickup with respect to the optical disk. In such a situation, because the adjustment range for the skew angle is small, and to reduce manufacturing costs, in many cases open-loop control is adopted in which no sensors, etc. are used; specifically, tilt control of the optical pickup is done by giving the stepping motor a control command of a prescribed number of steps from a base position that serves as the base for the control. With such open-loop control, one cannot acquire the present position of the optical pickup by a sensor, etc. and add it to the control command, so if the optical pickup is to be moved to the center position where the pre-measured jitter amount of the output signal of the optical pickup is at its minimum, a procedure such as the following is adopted.
Taking the number of steps to give a control command from the base position as far as the maximum feed position of the stepping motor to be 100 steps and the number of steps to give a control command from the base position to the center position to be 50 steps, together with starting the optical disk device, a control command of 100 steps toward the base position is input to the stepping motor, and the optical pickup moves to the base position. Next, a control command of 50 steps from the base position toward the maximum feed position is input to the stepping motor, and the optical pickup is positioned in the center position.
By performing such control, when the optical pickup is center-positioned, it first is returned to the base position and then is positioned to the center position, which provides the advantage that the optical pickup can be surely centered at startup or when a reset is made, regardless of the position of the optical pickup when the optical disk device stops.
However, in the above-described optical pickup position control method, there is the problem that even though the optical pickup may reach the base position, depending on the position of the optical pickup when the optical disk device stops, the stepping motor will continue its feed operation according to the control command, so the stepping motor of the feed mechanism of the optical pickup will get out of step, generating out-of-step noise. That is, if for example the optical pickup is in the feed position corresponding to 10 steps of the stepping motor from the base position when during operation of the optical disk a system restart is requested by pressing the reset button, etc., and the optical disk device stops, then upon restart a 100-step control command toward the base position is input to the stepping motor, and the stepping motor initiates feed operation of the optical pickup. Then the stepping motor performs the right feed operation for the first 10 steps, and for the remaining 90 steps the optical pickup reaches the base position, and out-of-step noise is continuously generated from the stepping motor.
It is an object of the present invention to provide an optical pickup position control method that can reduce the out-of-step noise generated from the stepping motor and can accurately position the optical pickup.
The optical pickup position control method of the present invention uses a stepping motor to control the relative position of an optical disk and an optical pickup and has a first procedure that gives said stepping motor a control command that moves said optical pickup, by a feed amount that is smaller than the maximum feed amount from a base position that is the base for the control as far as the maximum feed position of said stepping motor, in the direction from said base position to said maximum feed position, a second procedure that gives said stepping motor a control command that moves said optical pickup by said maximum feed amount in the direction toward said base position, and a third procedure that gives said stepping motor a control command that moves said optical pickup in the direction from said base position toward said maximum feed position by a center position feed amount from said base position as far as the center position that yields the pre-measured optimum jitter characteristics of the output signal of said optical pickup. The center position feed amount in the third procedure is obtained by using a standard disk to measure, in the stage of manufacturing the disk device, the center position at which the jitter characteristics of the optical pickup are at their best. The center position feed amount that is obtained is stored in an E2PROM or other memory provided in the optical disk device and is called and used as necessary in executing the optical pickup position control method of the present invention.
In positioning by open-loop control, the optical pickup position control method of this invention is adopted in the following cases.
(1) If a restart is done during execution of the optical pickup position control method of this invention.
(2) If during execution of the optical pickup position control method of this invention the master switch of the optical disk device is turned off and the supply of power to the optical disk device is cut off.
(3) If, in operating the optical disk device, detection of recorded information is done by the optical pickup at a position displaced from the normal center position.
In accordance with the method of the present invention, by the fact that before the second procedure a first procedure is carried out in which a control command is given for a feed amount, in the direction from the base position to the maximum feed position, that is smaller than the maximum feed amount, even if upon restart the optical pickup is near the base position, by the first procedure the optical pickup first moves in the direction from the base position to the maximum feed position. Therefore one can reduce the out-of-step condition of the stepping motor in the second procedure by the portion it moved in the first procedure, the time during which out-of-step noise is continuously generated can be reduced, and by the second procedure the optical pickup can be returned surely to its base position. In addition, because the optical pickup is returned to its base position by the second procedure, the optical pickup can be surely positioned in the center position just by, in the third procedure, giving the stepping motor the center position feed amount as a control command.
In the foregoing, it is desirable that the feed amount in the first procedure be the difference between the maximum feed amount and the center position feed amount. By thus setting the feed amount in the first procedure to the difference between the maximum feed amount and the center position feed amount, even if a restart is done in a state in which the optical pickup is positioned at the center position, it will become equal to the maximum feed amount if said difference is added to the center position after the restart. Therefore, the optical pickup can be moved to the maximum feed position by the feed position due to the first procedure, and even if feeding is done by the maximum feed amount of the second procedure, the optical pickup can be returned to the base position without getting out of step. Also, if, following said third procedure, an optimum position adjustment procedure is performed that detects the jitter value of the output signal of the optical pickup, position-adjusts said optical pickup so that the jitter characteristics for said optical disk are optimum, and stores the adjustment feed amount from the base position for the adjusted optimum position, it is desirable that it have a fourth procedure that, upon termination of recording and/or playback of information by the optical pickup, gives the stepping motor a control command that moves the optical pickup by the difference between this adjustment feed amount and the center position feed amount.
Thus, the optimum position adjustment procedure is a procedure that is carried out because it cannot be said that the center position set based on the measurement using a standard disk is necessarily the optimum position in relation to the optical disk that is actually used; it can be done by user operation, but it can also be done automatically by the optical disk device following the third procedure. This is because the optical disk that is actually used may be different from the standard disk because of deviation of the center hole, warping of the disk, etc. In addition, the adjustment position feed amount is stored in a RAM, etc. provided on the optical disk device, and it may be erased after termination of the fourth procedure. In addition, xe2x80x9cupon termination of recording and/or playback of information by the optical pickupxe2x80x9d in the fourth procedure refers to cases in which a system that includes the optical disk device is initialized, by for example a reset button, while information recorded on the optical disk is being played back or information is being recorded onto the disk. Because such a fourth procedure moves the optical pickup by the difference between this adjustment feed amount and the center position feed amount upon termination of recording and/or playback of information by the optical pickup, before the system is shut down by the reset button, etc., the optical pickup can be returned to the center position, and the aforesaid generation of out-of-step noise can be surely suppressed when the first procedure and second procedure are executed upon restart.
Furthermore, it is desirable that control of the relative position of said optical disk and optical pickup be tilt control between the two, and it is desirable that said tilt control be control of said optical disk in the radial skew direction. That is, there is available as the optical pickup positioning control in an optical disk device tracking servo control, focus servo control, slide feed control, and tilt control, and closed-loop control, in which the control is done while detecting the output signal from the optical pickup, is adopted in tracking servo control, focus servo control, and slide feed control. In contrast to this, normally tilt control is done only as initial control upon startup, and open-loop control is often adopted for reasons of cost, etc., and it is desirable for adopting this invention. For tilt control, one could have control in the tangential skew or radial skew direction, and the precision of detection of the optical pickup due to variability in the optical disk, such as warping, bias of the center hole, etc. is greatly improved by doing control in the radial skew direction. Therefore, by performing control in the radial skew direction in this way, it is possible to control the position of the optical pickup by the necessary minimum and to great precision.